A percussion jig of the general type to which the invention relates is disclosed in the textbook by Rittinger, Lehrbuch der Aufbereitungskunde, FIG. 297a.
In this known percussion jig a light material discharge chute extends over the whole breadth of the settling tank and is movable upwards and downwards with the settling tank. During operation the walls of the settling tank are located below the surface of the settling fluid. Thus the chute is completely immersed in the settling fluid.
Between the settling tank which is moved up and down and the wall of the settlement tub which contains the settling tank there is a space filled with settling fluid. When the settling tank and the chute connected thereto move upwards, a certain negative pressure occurs in the space below the chute with the consequence that settling fluid is sucked out of an adjacent following or downstream settlement tub into the space between the two settling tanks. This stream of fluid also carries particles of material with it out of the settling tank and into the aforementioned space, resulting in the depositing of undesirable faulty material there. A further disadvantage is that considerable wear is produced by the faulty material being sucked through sealed gaps.
The object of the invention, therefore, is to construct a percussion jig of the type referred to, but which avoids the undesirable suction and pressure conditions described above which occu below the chute during the upward and downward movement of the settling tank.